It has heretofore been known that titanium based catalysts composed of a titanium compound and an organoaluminum compound, or vanadium based catalysts composed of a vanadium compound and an organoaluminum compound are used as catalyst for the preparation of .alpha.-olefin polymers, for example, ethylene polymers or ethylene/.alpha.-olefin copolymers.
Generally, ethylene/.alpha.-olefin copolymers obtained with the titanium based catalysts have a broad molecular weight distribution and a broad composition distribution and are poor in transparency, surface non-tackiness and dynamical properties. Ethylene/.alpha.-olefin copolymers obtained with the vanadium based catalyst have a narrow molecular weight distribution and a narrow composition distribution in comparison with the ethylene/.alpha.-olefin copolymers obtained with the titanium based catalysts, and show a fairly good improvement in transparency, surface non-tackiness and dynamical properties, but said catalyst are low in polymerization activities and the resulting ethylene/.alpha.-olefin copolymers require deashing operation. Thereafter, it is desired that catalyst systems further improved in these properties and developed to make their appearance.
Under such circumstances, on the one hand, there have been proposed recently processes for the preparation of ethylene/.alpha.-olefin copolymers using catalysts composed of zirconium compounds and aluminoxanes as a new type of Ziegler catalysts for olefin polymerization.
For example, Japanese Patent L-O-P Publn. No. 19309/1983 disclosed a process for the preparation of ethylene/.alpha.-olefin copolymers, which process comprises polymerizing ethylene and one or at least two C.sub.3 -C.sub.12 .alpha.-olefins at a temperature of from -50.degree. C. to 200.degree. C. in the presence of a catalyst composed of a transition metal containing compound represented by the following formula EQU (Cyclopentadienyl).sub.2 MeRHal
wherein R is cyclopentadienyl, C.sub.1 -C.sub.6 alkyl or halogen, Me is a transition metal and Hal is halogen, and a linear aluminoxane represented by the following formula EQU Al.sub.2 OR.sub.4 (Al(R)--O).sub.n
wherein R is methyl or ethyl, and n is a number of from 4 to 20, or a cyclic aluminoxane represented by the following formula ##STR1## wherein R and n are as defined above. This patent L-O-P publication teaches that in order to regulate the density of the resulting polyethylene, the polymerization of ethylene should be carried out in the presence of small quantities of up to 10% by weight of fairly long chain .alpha.-olefins or mixtures thereof.
Japanese Patent L-O-P Publn. No. 95292/1984 discloses an invention relating to processes for preparing a linear aluminoxanes represented by the following formula ##STR2## wherein n is a number of from 2 to 40, and R is C.sub.1 -C.sub.6 alkyl, and a cyclic aluminoxane represented by the following formula ##STR3## wherein n and R are as defined above.
This patent L-O-P publication describes that when the polymerization of ethylene is carried out in the presence of a mixture comprising the aluminoxane prepared by the process of said publication, for example, methyl aluminoxane, and a bis(cyclopentadienyl)zirconium compound or a bis(cyclopentadienyl)titanium compound, there are obtained at least twenty-five million grams of polyethylene per 1 g of the transition metal and per 1 hour.
Japanese Patent L-O-P Publn. No. 35005/1985 discloses a process for preparing olefin polymerization catalyst, which comprises first reacting an aluminoxane compound represented by the following formula ##STR4## wherein R.sup.1 is C.sub.1 -C.sub.10 alkyl, and R.sup.0 is R.sup.1 or R.sup.0 represents --O--by linkage, with a magnesium compound, and then chlorinating the reaction product, followed by treatment with a compound of Ti, V, Zr or Cr. This patent L-O-P publication describes that the catalysts prepared by the process are particularly suitable for use in copolymerization of ethylene and C.sub.3 -C.sub.12 .alpha.-olefins.
Japanese Patent L-O-P Publn. No. 35006/1985 discloses a combination of (a) two or more dissimilar mono-, di- or tri-cyclopentadienyls or their derivatives of transition metals and (b) an aluminoxane as a catalyst for preparation of reactor blended polymers. Example 1 of this Patent L-O-P publication discloses that ethylene and propylene are polymerized in the presence of a catalyst composed of bis(pentamethylcyclopentadienyl)dimethyl zirconium and an aluminoxane to obtain polyethylene having a number average molecular weight of 15,300, a weight average molecular weight of 36,400 and containing 3.4% of the propylene component. In Example 2 of this patent L-O-P publication, ethylene and propylene are polymerized in the presence of a catalyst composed of bis(pentamethylcyclopentadienyl)zirconium dichloride, bis(methylcylcopentadienyl)zirconium dichloride and an aluminoxane to obtain a blend of polyethylene and an ethylene/propylene copolymer consisting of a toluene-soluble portion having a number average molecular weight of 2,200 and a weight average molecular weight of 11,900 and containing 30 mol% of the propylene component and a toluene-insoluble portion having a number average molecular weight of 3,000 and a weight average molecular weight of 7,400 and containing 4.8 mol% of the propylene component, said blend having a number average molecular weight of 2,000 and a weight average molecular weight of 8,300 and containing 7.1 mol% of the propylene component. Similarly, Example 3 discloses a blend of LLDPE and an ethylene/propylene copolymer consisting of a soluble portion having a molecular weight distribution (Mw/Mn) of 4.57 and containing 20.6 mol% of the propylene component and an insoluble portion having a molecular weight distribution of 3.04 and containing 2.9 mol% of the propylene component.
Japanese Patent L-O-P Publn. No. 35007/1985 discloses a process wherein ethylene alone is polymerized, or ethylene and an .alpha.-olefin of 3 or more carbon atoms are copolymerized in the presence of a catalyst system containing a metallocene and a cyclic aluminoxane represented by the following formula ##STR5## wherein R is an alkyl group of 1 to 5 carbon atoms, and n is an integer of 1 to about 20, or a linear aluminoxane represented by the following formula EQU R(R--Al--O).sub.n Al R.sub.2
wherein R and n are as defined above.
According to this patent L-O-P publication, the polymers obtained in this manner have a weight average molecular weight of about 500 to about 1,400,000 and a molecular weight distribution of 1.5 to 4.0.
Japanese Patent L-O-P Publn. No. 35008/1985 discloses that polyethylene or ethylene/C.sub.3 -C.sub.10 .alpha.-olefins copolymers having a wide molecular weight distribution are prepared by using a catalyst system comprising at least two metallocenes and aluminoxane. This patent L-O-P publication indicates that the copolymers obtained in this manner have a molecular weight distribution (Mw /Mn) of 2-50.
Japanese Patent L-O-P Publns. Nos. 260602/1985 and 130604/1985 propose processes for polymerizing olefins by using catalysts formed from a transition metal compound and a mixed organoaluminum compound comprising a transition metal compound, aluminoxane and an organoaluminum compound, and disclose that polymerization activity per unit transition metal improves by the addition of the organoaluminum compound.
Japanese Patent L-O-P Publn. No. 36390/1987 teaches that aluminoxanes are obtained by reaction of organoaluminum compounds with iron compounds containing water of crystallization, Japanese Patent L-O-P Publn. No. 148491/1987 teaches that aluminoxanes may be obtained by reaction of organoaluminum compounds with compounds containing water of crystallization selected from the group consisting of magnesium compounds, nickel compounds and lanthanide compounds, and Japanese Patent L-O-P Publns. Nos. 56507/1988 and 56508/1988 teach that aluminoxanes can be obtained by reaction of water directly with organoaluminum compounds in inert hydrocarbon solvents utilizing a high speed, high shearing ability induction type impeller or an ultrasonic wave.
In preparing .alpha.-olefin (co)polymers in the manner now described, when the aluminoxane compounds are used as one component of the catalyst therefor, .alpha.-olefin (co)polymers having a narrow molecular weight distribution and a narrow composition distribution can be obtained with excellent polymerization activity.
However, a great desideratum for the industry concerned is the advent of such aluminoxane type organoaluminum compounds as having excellent polymerization activity on .alpha.-olefin and as being capable of giving olefin (co)polymers having a narrow molecular weight distribution and a narrow composition distribution.
In this connection, known aluminoxane compounds used hitherto in olefin polymerization, even when they are used in a state of liquid or solid, were prepared and recovered as those which are soluble in hydrocarbon solvents such as benzene or toluene, and their molecular weight was determined by cryoscopic methods after dissolving them in benzene and, moreover, a structure of said aluminoxane was decided by measuring a freezing point thereof in benzene.
In light of the foregoing points, the present inventors prosecuted extensive researches and eventually have accomplished the present invention on the basis of their fining that novel organoaluminum oxy-compounds prepared from known aluminoxanes or organoaluminum compounds which have not been known at all hitherto and which are insoluble or sparingly soluble in benzene and toluene exhibit excellent catalytic activities in olefin polymerization.